What is termed the lift bed method for treating liquids is disclosed, for example, by DE 2950875 A1 (=U.S. Pat. No. 4,461,706). This relates to a countercurrent flow method for treating liquids with adsorption media by loading the adsorption media in upward flow, the lower part of the adsorption medium mass being present as fluidized bed and the upper part as fixed bed, regenerating the loaded adsorption media in downward flow and backwashing in upward flow by subdividing the filter space into at least two chambers separated by liquid-permeable bases, connecting these chambers to one another via pipes which bridge the liquid-permeable bases, permit the transport of adsorption medium and are provided with a shutoff element, distributing the adsorption medium among the chambers and before and/or during the individual working phases setting defined filling levels in the individual chambers by transferring adsorption medium from one chamber via the pipes bridging the liquid-permeable bases to the other chamber by means of liquid to be treated, regeneration medium or backwash liquid.
In many cases it is expedient, in addition to the ion-exchanger resins, to use an inert material. In this manner, the risk of blocking nozzle slots is substantially excluded.
The advantages of the lift bed method according to DE 2 950 875 A1 (=U.S. Pat. No. 4,461,706) over conventional methods were higher regeneration efficiency in association with reduction of the chemical requirement, reduction of the waste water amount, internal backwashing, and also flexibility, versus the introduction of impurities in the form of suspended substances and also simultaneous insensitivity to load variations. However, such lift bed methods require a greater capital expenditure and in addition require increased closed-loop and open-loop control expenditure.
It was an object of the present invention to optimize the proven method according to DE 2 950 875 A1 (=U.S. Pat. No. 4,461,706) with respect to said disadvantages. It was found that highly efficient demineralization plants are obtained when the cation filter is operated in the lift bed mode and the anion filter or filters are operated in cocurrent flow mode and, in addition, the ion-exchanger resins used have a monodisperse particle size distribution.